Drilling fluids that include water-soluble acid catalyst precursors or reaction products of such and uses for such drilling fluids

ABSTRACT

In accordance with one or more embodiments of the present disclosure, a drilling fluid may include a base fluid and one or more formaldehyde-based resins. The drilling fluid may further comprise one or more water-soluble acid catalyst precursors or the reaction products of such water-soluble acid catalyst precursors. The base fluid may include an aqueous or non-aqueous solution. The present disclosure also describes sealed subterranean petroleum formations that include such drilling fluids and methods for sealing subterranean wellbores by utilizing such drilling fluids.

BACKGROUND Field

The present disclosure relates to wellbore drilling technology and, morespecifically, to drilling fluids utilized in wellbore drilling.

Background

Drilling operations to, for example, drill wellbores for hydrocarbonextraction may include the practice of continuously circulating adrilling fluid (sometimes referred to as a drilling mud) through theformed wellbore during the drilling operation. The drilling fluid may bepumped into the drill pipe and to the bottom of the borehole where thedrilling fluid then flows upwardly through an annular space between thewellbore wall and the drill pipe, and finally returns to the surface andflows out of the wellbore where it is recovered for secondaryprocessing. During drilling, the drilling solids, such as portions ofthe drilled geological formation, may be carried by the drilling fluidfrom at or near the bottom of the wellbore to the surface. When thedrill head encounters an area of reduced formation pressure, such as afracture, drilling fluid can leak out of the wellbore in what is knownas a “lost circulation zone.” The consequences of encountering a lostcirculation zone can range from drilling fluid leaks to drill head anddrill string damage. Lost circulation zones may even lead to blowoutsand loss of life. Remediation of a lost circulation zone generallyrequires the introduction of a sealing composition into the wellbore.However, this process is resource-intensive and time consuming.

BRIEF SUMMARY

Faster and more efficient lost circulation zone remediation techniquesare desired. It has been discovered that drilling fluids may befabricated which can be pumped in a liquid state and converted to a gelas desired. The drilling fluid, in gel form, may then be suitable toseal the porous areas, cracks, fractures, or other geological featureswhich cause the lost circulation zone. According to one or moreembodiments presently described, a drilling fluid which is gellable mayinclude a base fluid and a formaldehyde-based resin. The introduction ofa water-soluble acid catalyst precursor to the drilling fluid mayinitiate the conversion of the water-soluble acid catalyst precursorinto a water-soluble acid catalyst. The formed water-soluble acidcatalyst may initiate conversion of the drilling fluid from a liquidstate to a gelled state. For example, the water-soluble acid catalystmay polymerize at least a portion of the formaldehyde-based resinspresent in the drilling fluid, which may cause the drilling fluid tobecome a gelled state material. Furthermore, it should be understoodthat while such drilling fluids may be suitable for use inloss-circulation zones, these drilling fluids may find applicability forother uses such as when controlled gelling of a drilling fluid isdesired.

In accordance with one or more embodiments of the present disclosure, adrilling fluid may include a base fluid and one or moreformaldehyde-based resins. The drilling fluid may further comprise oneor more water-soluble acid catalyst precursors or the reaction productsof such water-soluble acid catalyst precursors. The base fluid mayinclude an aqueous or non-aqueous solution. The weight ratio of the oneor more formaldehyde-based resins to the base fluid may be from 1:100 to50:100. The drilling fluid may optionally include polyvinyl alcohol orvinyl alcohol copolymers, where if the polyvinyl alcohol or vinylalcohol copolymers are present in the drilling fluid, the weight ratioof the sum of the polyvinyl alcohol or vinyl alcohol copolymers to thetotal weight of the drilling fluid may be less than or equal to 1.5:100.The weight ratio of the sum of the one or more water-soluble acidcatalyst precursors and the reaction products of such water-soluble acidcatalyst precursors to the total weight of the drilling fluid may befrom 0.5:100 to 20:100.

In accordance with one or more embodiments of the present disclosure, asealed subterranean petroleum formation may include a subterraneanwellbore positioned adjacent a subterranean petroleum formation and adrilling fluid positioned in the subterranean wellbore. The drillingfluid may include a base fluid, one or more formaldehyde-based resins,and optionally polyvinyl alcohol or vinyl alcohol copolymers. Thedrilling fluid may further include one or more water-soluble acidcatalyst precursors or the reaction products of such water-soluble acidcatalyst precursors. The base fluid may include an aqueous ornon-aqueous solution. The weight ratio of the one or moreformaldehyde-based resins to the base fluid may be from 1:100 to 50:100.If the polyvinyl alcohol or vinyl alcohol copolymers are present in thedrilling fluid, the weight ratio of the sum of the polyvinyl alcohol orvinyl alcohol copolymers to the total weight of the drilling fluid maybe less than or equal to 1.5:100. The weight ratio of the sum of the oneor more water-soluble acid catalyst precursors and the reaction productsof such water-soluble acid catalyst precursors to the total weight ofthe drilling fluid may be from 0.5:100 to 20:100.

In accordance with yet more embodiments of the present disclosure, amethod for sealing a subterranean wellbore may include introducing adrilling fluid into a subterranean wellbore and introducing one or morewater-soluble acid catalyst precursors to the drilling fluid. Thewater-soluble acid catalyst precursor may form a water-soluble acid inthe drilling fluid in an amount operable to transition the drillingfluid from a liquid state to a gelled state. The subterranean wellboremay be positioned adjacent to a subterranean petroleum formation. Thedrilling fluid may include a base fluid, one or more formaldehyde-basedresins, and optionally polyvinyl alcohol or vinyl alcohol copolymers.The base fluid may include an aqueous or non-aqueous solution. Theweight ratio of the one or more formaldehyde-based resins to the basefluid may be from 1:100 to 50:100. If the polyvinyl alcohol or vinylalcohol copolymers are present in the drilling fluid, the weight ratioof the sum of the polyvinyl alcohol or vinyl alcohol copolymers to thetotal weight of the drilling fluid may be less than or equal to 1.5:100.

ABBREVIATIONS

One or more abbreviations are used in the present application, in which:

ASTM=American Society for Testing and Materials;

API=American Petroleum Institute;

C_(x)=carbon chain of x length;

cP=centipoises;

° F.=degrees Fahrenheit;

g=grams;

lb/100 ft²=pounds per 100 square feet;

min.=minutes;

ml=milliliters;

Pa=Pascals;

PAC L=polyanionic cellulose polymer;

PCF=pounds per cubic foot;

psi=pounds per square inch;

rpm=revolutions per minute;

sec.=seconds;

SOBM=synthetic oil based mud; and

wt. %=weight percent.

DETAILED DESCRIPTION

The present disclosure is directed to drilling fluids which may besuitable for use in sealing wells. The present disclosure is furtherdirected to the fabrication of such drilling fluids, as well as the usesof such. According to one or more embodiments of the present disclosure,a drilling fluid is provided that may include a base fluid and one ormore formaldehyde-based resins. The drilling fluid may further includeone or more gel initiator additives such as water-soluble acid catalystprecursors or the reaction products of such.

In one or more embodiments, the base fluid may comprise an aqueoussolution. For example, the aqueous solution may include one or more ofdeionized, tap, distilled, or fresh waters; natural, brackish, orsaturated salt waters; natural, salt dome, hydrocarbon formationproduced, or synthetic brines; filtered or untreated seawaters; mineralwaters; or other potable or non-potable waters containing one or moredissolved salts, minerals, or organic materials. In one or moreembodiments, the base fluid may comprise at least 80 wt. %, at least 90wt. %, at least 95 wt. %, at least 99 wt. %, or even at least 99.9 wt. %of water.

According to additional embodiments, the base fluid may include anon-aqueous solution. The non-aqueous solution may include one or morecrude oils or crude oil derivatives such as gasoline, diesel, kerosene,bunker fuel, jet fuel, naptha, or any fraction of a crude oil. Forexample, in some embodiments non-aqueous drilling fluids may be referredto as synthetic oil based muds (also referred to in the presentdisclosure as oil-based muds and SOBMs). Synthetic oil-based muds mayinclude crude oil derivatives that have been chemically treated,altered, or refined to enhance certain chemical or physical properties.In comparison, partially-refined crude oil, which may contain severalclasses (for example, alkane, aromatic, sulfur-bearing,nitrogen-bearing) of thousands of individual compounds, a SOBM maycomprise one class with only tens of individual compounds (for example,ester compounds in a C₈₋₁₄ range). Examples of materials used as basefluids for SOBMs include linear alpha olefins, isomerized olefins, polyalpha olefins, linear alkyl benzenes, and vegetable andhydrocarbon-derived ester compounds. In one or more embodiments, thebase fluid may comprise at least 80 wt. %, at least 90 wt. %, at least95 wt. %, at least 99 wt. %, or even at least 99.9 wt. % of a non-watermaterial such as an oil.

According to some additional embodiments of the present disclosure, thedrilling fluid may be characterized as an emulsion. The emulsion may bea mixture of the aqueous and non-aqueous base fluids or it may be amixture of the base fluid and a natural fluid such as water ingress intothe fluid. The drilling fluid emulsion may include a surfactant. In suchembodiments, the base fluid may comprise water and a non-water componentsuch as an oil. In one or more embodiments, the base fluid may compriseat least 80 wt. %, at least 90 wt. %, at least 95 wt. %, at least 99 wt.%, or even at least 99.9 wt. % of the combination of water and anon-water material such as an oil.

According to one or more embodiments of the present disclosure, theformaldehyde-based resin may be any resin which includes formaldehyde.For example, the formaldehyde-based resin may be one or more of amelamine-formaldehyde resin, a urea-formaldehyde resin, or aphenol-formaldehyde resin. A urea-formaldehyde resin should beunderstood to include any products of the reaction of urea andformaldehyde. A phenol-formaldehyde resin should be understood toinclude any products of the reaction of a phenol or substituted phenolwith formaldehyde. A melamine-formaldehyde resin should be understood toinclude any products of the condensation of formaldehyde and melamine.Suitable commercially available melamine-formaldehyde resins, withoutlimitation, may include MELFORES 101P (commercially available fromChemanol). Suitable formaldehyde based resins may be distributed aspowders, liquids, or dispersions. Suitable formaldehyde-based resins maybe formed in-situ in the drilling fluid by the reaction of melamine,phenol, or urea with formaldehyde.

The weight ratio of the one or more formaldehyde-based resins to thebase fluid may be from 1:100 to 50:100. For example, the weight ratio ofthe one or more formaldehyde resins to the base fluid may be from0.1:100 to 5:100, from 5:100 to 10:100, from 10:100 to 15:100, from15:100 to 20:100, from 20:100 to 25:100, or from 25:100 to 30:100, from30:100 to 35:100, from 35:100 to 40:100, from 40:100 to 45:100, from45:100 to 50:100, or any combination of these. It should be understoodthat the sum of the any one or more presently disclosed formaldehydebased resins may be present in a weight ratio with respect to the basefluid in any of the disclosed ranges. For example, a singleformaldehyde-based resin may be in one of the disclosed weight ratioswith respect to the base fluid, or the sum of a combination of disclosedformaldehyde-based resins may be in one of the disclosed weight ratioswith respect to the base fluid.

The drilling fluid may become gelled when contacted by the reactionproducts of the one or more gel initiator additives. The one or more gelinitiator additives may include one or more water-soluble acid catalystprecursors. As used in this disclosure, a “water-soluble acid catalystprecursor” may refer to any compound which is water-soluble and iscapable of reacting to form an acid catalyst following its incorporationinto the drilling fluid. As used in this disclosure, the “reactionproducts” of the water-soluble acid catalyst precursor may refer to thisformed acid catalyst. As presently described, the reaction products areformed from the acid catalyst precursor in the drilling fluid (that is,not in advance of the acid catalyst precursor being mixed with the othercomponents of the drilling fluid). Without being limited by theory, theformed acid catalyst is believed to be operable to initiatepolymerization of the formaldehyde-based resin. It is believed that thewater-soluble acid catalyst precursor is not directly operable toinitiate polymerization of the formaldehyde-based resin and that thewater-soluble acid catalyst precursor must first form the water-solubleacid catalyst before initiating polymerization of the formaldehyde-basedresin.

According to some embodiments, the one or more water-soluble acidcatalyst precursors may undergo a hydrolysis reaction with water to forman acid catalyst, such as a carboxylic acid. For example, the one ormore water-soluble acid catalyst precursors may be ethyl lactate. Ethyllactate is known to undergo a hydrolysis reaction to form lactic acid,as is shown in Reaction 1.

C₅H₁₀O₃+H₂O→CH₃CHOCO₂H+C₂H₅OH  Reaction 1:

According to one or more embodiments, it is believed to be advantageousto use a water-soluble acid catalyst precursor, as opposed to a materialthat is not water-soluble or an acid catalyst precursor, due at least totheir ability to form an acid catalyst in-situ and thereby enablepolymerization of the formaldehyde-based resin in a delayed orcontrollable manner. For example, in some circumstances, introduction ofa water-soluble acid catalyst (that is, not a catalyst precursor) mayresult in overly rapid polymerization. Water solubility may beadvantageous because it may allow for more uniform dispersion of theacid catalyst precursor throughout at least the aqueous phase portionsof the drilling fluid.

According to some embodiments of the present disclosure, thewater-soluble acid catalyst precursor may include a water-solublehydrolysable ester. In some embodiments, the water-soluble hydrolysableester may include one or more of ethyl lactate, diethylene glycoldi-formate, ethyl acetate, ethyl formate, ethylene glycol diacetate, ordiethylene glycol di-lactate. The water-soluble hydrolysable ester mayinclude ethyl lactate. In one or more embodiments, at least 80 wt. %, atleast 90 wt. %, at least 95 wt. %, at least 99 wt. %, or even at least99.9 wt. % of the water-soluble acid catalyst precursor may includewater-soluble hydrolysable ester.

The water-soluble hydrolysable ester or the reaction products of suchmay be present in an amount such that the weight ratio of the sum of theone or more water-soluble acid catalyst precursors and the reactionproducts of such to the total weight of the drilling fluid is from0.1:100 to 20:100. For example, the weight ratio of the sum of the oneor more water-soluble acid catalyst precursors and the reaction productsof such to the total drilling fluid may be from 0.1:100 to 0.5:100, orfrom 0.5:100 to 2:100, or from 2:100 to 5:100, or from 5:100 to 10:100,or from 10:100 to 15:100, or from 15:100 to 20:100, or any combinationof these.

The water-soluble acid catalyst precursor and the reaction products ofsuch may be present in an amount such that the pH of the drilling fluid,at a hydrolysis benchmark time after initial contacting of thewater-soluble acid catalyst precursor with the base fluid, is less thanor equal to 6, less than or equal to 5, less than or equal to 4, lessthan or equal to 3, less than or equal to 2. The hydrolysis benchmarktime may be from 0.5 hours (hr) to 24 hr, for example, the hydrolysisbenchmark time may be 0.5 hr, 1 hr, 2 hr, 4 hr, 8 hr, 12 hr, 16 hr, 20hr, 24 hr, from 0.5 hr to 1 hr, from 1 hr to 2 hr, from 2 hr to 4 hr,from 4 hr to 6 hr, from 6 hr to 8 hr, from 8 hr to 10 hr, from 10 hr to12 hr, from 12 hr to 16 hr, from 16 hr to 20 hr, from 20 hr to 24 hr, orany combination of these. Without being limited by theory, it isbelieved that the water-soluble acid catalyst precursor is not acidicand may not make the drilling fluid acidic immediately.

According to some embodiments of the present disclosure, the drillingfluid may include one or more weighting agents. The weighting agent mayinclude, for example, one or more of barite, hematite, calciumcarbonate, siderite, or limenite. The weight ratio of the one or moreweighting agents to the base fluid may be from 10:100 to 300:100, from1:100 to 10:100, from 10:100 to 25:100, from 25:100 to 50:100, from50:100 to 100:100, from 100:100 to 150:100, from 150:100 to 200:100,from 200:100 to 250:100, from 250:100 to 300:100, from 300:100 to350:100, from 350:100 to 400:100, from 400:100 to 450:100, from 450:100to 500:100, or any combination of these.

According to some embodiments of the present disclosure, the drillingfluid may include a rheology modifier. The rheology modifier mayinclude, for example, one or more of bentonite, montmorillonite, sodiumcarbonate, polymers, carboxymethylcellulose (CMC), starch, orphosphorylates. The polymer may include one or both of guar gum(sometimes called XC-Polymer) or polyanionic cellulose polymer (such asPAC L, commercially from Halliburton). The weight ratio of the rheologymodifier to the base fluid may be from 0.001:100 to 10:100. For example,the weight ratio may be from 0.001:100 to 0.005:100, from 0.005:100 to0.01:100, from 0.01:100 to 0.5:100, from 0.5:100 to 1:100, from 0.5:100to 1:100, from 1:100 to 2:100, from 2:100 to 3:100, from 3:100 to 4:100,from 4:100 to 5:100, from 5:100 to 6:100, from 6:100 to 7:100, from8:100 to 9:100, from 9:100 to 10:100, any combination of these. Theconcentration of the rheology modifier in the drilling fluid may be from0.1 pounds per barrel (ppb) to 20 ppb. For example, the concentrationmay be from 0.1 ppb to 0.5 ppb, from 0.5 ppb to 1 ppb, from 1 ppb to 1.5ppb, from 1.5 ppb to 2 ppb, from 2.5 ppb to 3 ppb, from 3 ppb to 4 ppb,from 4 ppb to 5 ppb, from 5 ppb to 6 ppb, from 6 ppb to 7 ppb, from 7ppb to 8 ppb, from 8 ppb to 9 ppb, from 9 ppb to 10 ppb, from 10 ppb to11 ppb, from 11 ppb to 12 ppb, from 12 ppb to 13 ppb, from 13 ppb to 14ppb, from 14 ppb to 15 ppb, from 15 ppb to 16 ppb, from 16 ppb to 17ppb, from 17 ppb to 18 ppb, from 18 ppb to 19 ppb, from 19 ppb to 20ppb, or any combination of these.

According to some embodiments of the present disclosure, the drillingfluid may include a basic additive. The basic additive may include oneor both of sodium hydroxide or potassium hydroxide. Without beinglimited by theory, it is believed that in some embodiments theformaldehyde-based resin may not cause the drilling fluid to gel at pHvalues greater than 6. It may be beneficial to keep the pH of thedrilling fluid as basic as possible until it is desired for the drillingfluid to gel.

In one or more embodiments, a standard drilling fluid may be convertedto an embodiment of the drilling fluid of this disclosure as a leak isdetected by addition of the acid precursor, causing subsequent gelling.The standard drilling fluid may have any characteristics expected of adrilling fluid such as a basic pH.

The weight ratio of the basic additive to the base fluid may be from0.001:100 to 5:100. For example, the weight ratio may be from 0.001:100to 0.005:100, from 0.005:100 to 0.01:100, from 0.01:100 to 0.5:100, from0.5:100 to 1:100, from 0.5:100 to 1:100, from 1:100 to 2:100, from 2:100to 3:100, from 3:100 to 4:100, from 4:100 to 5:100, or any combinationof these. The concentration of the basic additive in the drilling fluidmay be from 0.1 pounds per barrel (ppb) to 10 ppb. For example, theconcentration may be from 0.1 ppb to 0.5 ppb, from 0.5 ppb to 1 ppb,from 1 ppb to 1.5 ppb, from 1.5 ppb to 2 ppb, from 2.5 ppb to 3 ppb,from 3 ppb to 4 ppb, from 4 ppb to 5 ppb, from 5 ppb to 6 ppb, from 6ppb to 7 ppb, from 7 ppb to 8 ppb, from 8 ppb to 9 ppb, from 9 ppb to 10ppb, or any combination of these.

According to some embodiments of the present disclosure, the drillingfluid may include cement. Generally, cements may be added to increasestrength but may have several disadvantages as compared with drillingfluids which contain little or no cement. Cements may have relativelylong cure times and may require the operator to re-drill through thecured cement. The ratio of cement to drilling fluid may be from 0.1:100to 0.5:100, from 0.5:100 to 1:100, from 1:100 to 2:100, from 2:100 to4:100, from 4:100 to 8:100, from 8:100 to 12:100, from 12:100 to 15:100,from 15:100 to 25:100, from 25:100 to 50:100, from 50:100 to 75:100,from 75:100 to 100:100, from 100:100 to 150:100, from 150:100 to200:100, or any combination of these.

According to some embodiments of the present disclosure, the drillingfluid may not include latex, or latex may be included in only relativelysmall amounts in the drilling fluid. If latex is present in the drillingfluid, the weight ratio of the latex to the total weight of the drillingfluid may be from 0:100 to 10:100, from 0:100 to 8:100, from 0:100 to6:100, from 0:100 to 4:100, from 0:100 to 2:100, from 0:100 to 1:100, oreven from 0:100 to 0.1:100. According to some embodiments, latex may notbe present in the drilling fluid. As used in this disclosure, “latex”may refer to rubber materials commercially available in aqueous latexform, such as aqueous dispersions or emulsions. These include naturalrubbers such as (cis-1,4-polyisoprene), modified types of these,synthetic polymers, or combinations of these. The synthetic polymers mayinclude styrene/butadiene rubber, cis-1,4-polybutadiene, high styreneresin, butyl rubber, ethylene/propylene rubber, neoprene rubber, nitrilerubber, cis-1,4-polyisoprenerubber, silicone rubber, chlorosulfonatedrubber, polyethylene rubber, epichlorohydrin rubber, fluorocarbonrubber, fluoro silicone rubber, polyurethane rubber, polyacrylic rubber,or polysulfide rubber. It is believed to be advantageous to use aminimal amount of latex at least for cost savings. It should beunderstood that while some conventional drilling fluids may requirelatex as an additive, the presently disclosed drilling fluids may notrequire latex for their desired functionality. The formaldehyde-basedresin and gel initiator additive of the presently disclosed drillingfluids may provide suitable gelling characteristics in the absence oflatex, or with relatively small amounts of latex included.

According to some additional embodiments of the present disclosure, thedrilling fluid may not include polyvinyl alcohol and vinyl alcoholcopolymers, or polyvinyl alcohol and vinyl alcohol copolymers may beincluded in only relatively small amounts in the drilling fluid. If thepolyvinyl alcohol or vinyl alcohol copolymers are present in thedrilling fluid, the weight ratio of the polyvinyl alcohol or vinylalcohol copolymers to the total weight of the drilling fluid may be from0:100 to 1.5:100, from 0:100 to 1:100, from 0:100 to 0.5:100, or evenfrom 0:100 to 0.1:100. In additional embodiments, the weight ratio ofthe combination of polyvinyl alcohol and vinyl alcohol copolymers to thetotal weight of the drilling fluid may be from 0:100 to 1.5:100, from0:100 to 1:100, from 0:100 to 0.5:100, or even from 0:100 to 0.1:100. Itis believed to be advantageous to use a minimal amount of polyvinylalcohol and vinyl alcohol copolymers at least for cost savings. Itshould be understood that while some conventional drilling fluids mayrequire polyvinyl alcohol or vinyl alcohol copolymers as an additive,the presently disclosed drilling fluids may not require polyvinylalcohol or vinyl alcohol copolymers for their desired functionality. Theformaldehyde-based resin and gel initiator additive of the presentlydisclosed drilling fluids may provide suitable gelling characteristicsin the absence of polyvinyl alcohol and vinyl alcohol copolymers, orwith relatively small amounts of polyvinyl alcohol and vinyl alcoholcopolymers included.

According to some embodiments or the present disclosure, the drillingfluid may be present in a gelled state, such as after it contains thereaction products of the presently disclosed gel initiator additive. Thereaction of the gel initiator additive may reduce the pH of the drillingfluid, which may cause gelation. The drilling fluid may be gelled orexist in a “gelled state” by meeting the criteria that the apparentviscosity at 300 rpm and 25° C. is greater than 50,000 cP. For example,conventional drilling fluids, or the disclosed drilling fluids prior tothe described reducing of pH, may have an apparent viscosity at 300 rpmand 25° C. of less than 500 cP, such as from 10 to 250 cP. Gelled statedrilling fluids, as presently described, may have an apparent viscosityat 300 rpm and 25° C. of at least 50,000 cP, such as at least 100,000cP, or even at least 150,000 cP. Apparent viscosity may be measuredaccording to API “RP 13B-1: Recommended Practice for Field TestingWater-based Drilling Fluids.”

According to some embodiments of the present disclosure, the drillingfluid may have (following introduction of the gel initiator additive) astorage modulus of at least 50 Pa. For example, the drilling fluid mayhave (following introduction of the gel initiator additive) a storagemodulus of at least 100 Pa, at least 150 Pa, at least 200 Pa, at least250 Pa, at least 300 Pa, at least 400 Pa, at least 500 Pa, from 1 Pa to10 Pa, from 10 Pa to 25 Pa, from 25 Pa to 50 Pa, from 50 Pa to 75 Pa,from 75 Pa to 100 Pa, from 100 Pa to 150 Pa, from 150 Pa to 200 Pa, from200 Pa to 300 Pa, from 300 Pa to 400 Pa, from 400 Pa to 500 Pa, from 500Pa to 600 Pa, from 600 Pa to 800 Pa, from 800 Pa to 1000 Pa, or anycombination of these. The storage modulus may be measured according toASTM “D5026-15, Standard Test Method for Plastics: Dynamic MechanicalProperties: In Tension.”

According to some embodiments of the present disclosure, the drillingfluid (after it contains the reaction products of the presentlydisclosed gel initiator additive) may have a 10 min. gel strength of atleast 10 lb/100 ft². For example, the gel strength of the drilling fluidmay be at least 15 lb/100ft², at least 20 lb/100ft², at least 40lb/100ft², at least 80 lb/100ft², at least 120 lb/100 ft², at least 160lb/100 ft², at least 200 lb/100 ft², or any combination of these. Thegel strength may be measured by the method API RP 13B-1: RecommendedPractice for Field Testing Water-based Drilling Fluids.

According to one or more embodiments of the present disclosure, thedrilling fluid may have a density of from 50 PCF to 160 PCF. Forexample, the density of the drilling fluid may be from 50 PCF to 80 PCF,from 80 PCF to 120 PCF, from 120 PCF to 160 PCF, or any combination ofthese. Drilling fluid density may be important to maintain theappropriate hydrostatic pressure in the wellbore. Inappropriate densitydrilling fluid can cause the flow of formation fluids into the wellboreduring drilling operations (such as kicks or blowouts). It should beunderstood that the density of the drilling fluid is not expected tochange as it transitions from a liquid to a gelled state.

In one or more embodiments, the presently disclosed drilling fluids maybe positioned in a wellbore during drilling of the wellbore. Accordingto some embodiments of the present disclosure, a sealed subterraneanpetroleum formation may include a subterranean wellbore positionedadjacent a subterranean petroleum formation and a drilling fluidpositioned in the subterranean wellbore. The sealed subterraneanpetroleum formation may not be completely sealed but may have itsleakage rate decreased relative to what it would be in the absence ofthe drilling fluids of the present disclosure.

According to some embodiments of the present disclosure, a method forsealing a well may include introducing a drilling fluid into asubterranean wellbore positioned adjacent to a subterranean petroleumformation and introducing to the drilling fluid one or more gelinitiator additives in an amount operable to reduce the pH of at least aportion of the drilling fluid to less than or equal to 6 to transitionthe drilling fluid from a liquid to a gelled state. For example, the pHmay be reduced to a pH range of from 0 to 1, from 1 to 2, from 2 to 3,from 3 to 4, from 4 to 5, from 5 to 6, or any combination of these. Itshould be understood that in some embodiments, the drilling fluid may befabricated by adding the various components in different orders. Forexample, the acid may be added to the base fluid before theformaldehyde-based resin is added to the base fluid to constitute thedrilling fluid.

According to some embodiments, the pH of the drilling fluid before theaddition of the gel initiator additive may be alkaline, such as in arange of from 8 to 12. For example, the pH of the drilling fluid beforethe addition of the gel initiator additive may be from 8 to 9, from 9 to10, from 10 to 11, from 11 to 12, or any combination of these. Withoutbeing limited by theory, it is believed that a starting pH of greaterthan 8 will enable normal drilling fluid operation and prevent prematuregelling of the drilling fluid.

In one or more embodiments, the one or more gel initiator additives maybe introduced to the drilling fluid inside of the subterranean wellbore.For example, a drilling fluid including the base fluid andformaldehyde-based resin may be inside the subterranean wellbore and thegel initiator additive may be subsequently pumped down into thewellbore. The gel initiator additive may be pumped near a site of asuspected leak, casing fracture, or site otherwise requiring sealing.Alternatively, the gel initiator additive may be pumped generally intothe drilling fluid in the wellbore and cause the bulk drilling fluid togel. In further embodiments, the one or more gel initiator additives maybe introduced to the drilling fluid outside of the subterraneanwellbore. Introducing the gel initiator additives to the drilling fluidoutside the subterranean wellbore may be more convenient. The drillingfluid including the gel initiator additive may then be pumped back downinto the subterranean wellbore before it has gelled.

EXAMPLES

Using the embodiments of the present disclosure, drilling fluidadditives were produced which exemplify the catalytic attributespresently described. It should be understood that the ensuing Examplesare illustrative of one or more embodiments presently disclosed, andshould not be construed as in any way as limiting on the appended claimsor other portions of the present application.

Example 1

A conventional 90 PCF aqueous drilling fluid was produced by combiningbentonite and water, and the mixture was allowed to sit for 4 hours. Thewater and bentonite were then mixed for twenty minutes. Then, in order,XC Polymer, PAC L, starch, NaOH, and barite were each added individuallywith five minutes of mixing after each addition. The concentrationsgiven in Table 1 are for the final drilling fluid.

TABLE 1 Additive wt. % Water 58.84 Bentonite 0.59 XC polymer 0.30 PAC L0.39 Starch 0.79 NaOH 0.01 Barite 38.98

The resultant conventional drilling fluid was then hot rolled for 16hours at 200° F. in an aging cell. After hot rolling, the conventionaldrilling fluid was allowed to cool and was then transferred to a mudcup. The conventional drilling fluid was subsequently subjected to avariety of standard rheological and filtration property tests at 120° F.The rheological and filtration properties are shown in Table 2.

TABLE 2 Measurement Value 600 rpm 80 lb/100 ft² 300 rpm 53 lb/100 ft²200 rpm 41 lb/100 ft² 100 rpm 28 lb/100 ft² 6 rpm 4 lb/100 ft² 3 rpm 3lb/100 ft² Plastic viscosity 27 cP Yield point 26 lb/100 ft² 10 sec. GelStrength 3 lb/100 ft² 10 min. Gel Strength 5 lb/100 ft² pH 10.3 APIfluid loss, 30 min 4 ml

As can be seen in from the data of Table 2, the conventional drillingfluid did not form a gel.

Example 2

To form a drilling fluid of some embodiments of the present disclosure,350 ml of the conventional drilling fluid of example 1 was mixed with 50g of powdered melamine formaldehyde resin (commercially available asMELFORES 101 P) for 5 minutes. Then, 5 g of ethyl lactate was added andthe solution was mixed for another 5 minutes.

The resultant gellable drilling fluid was then static aged in a curingchamber at 200° F. and 1000 psi for 16 hours. After removal from thecuring chamber, it was observed that the gellable drilling fluid hadformed a gelled solid. The gelled solid maintained a cylindrical shapewith no external support. It had well defined corners and no observablesagging along the vertical walls.

It is noted that recitations in the present disclosure of a component ofthe present disclosure being “operable” or “sufficient” in a particularway, to embody a particular property, or to function in a particularmanner, are structural recitations, as opposed to recitations ofintended use. More specifically, the references in the presentdisclosure to the manner in which a component is “operable” or“sufficient” denotes an existing physical condition of the componentand, as such, is to be taken as a definite recitation of the structuralcharacteristics of the component.

Having described the subject matter of the present disclosure in detailand by reference to specific embodiments, it is noted that the variousdetails disclosed in the present disclosure should not be taken to implythat these details relate to elements that are essential components ofthe various embodiments described in the present disclosure. Further, itwill be apparent that modifications and variations are possible withoutdeparting from the scope of the present disclosure, including, but notlimited to, embodiments defined in the appended claims.

It is noted that one or more of the following claims utilize the term“where” as a transitional phrase. For the purposes of defining thepresent subject matter, it is noted that this term is introduced in theclaims as an open-ended transitional phrase that is used to introduce arecitation of a series of characteristics of the structure and should beinterpreted in like manner as the more commonly used open-ended preambleterm “comprising.”

1. A drilling fluid comprising: a base fluid comprising an aqueous ornon-aqueous solution; one or more formaldehyde-based resins, wherein theweight ratio of the one or more formaldehyde-based resins to the basefluid is from 1:100 to 50:100; optionally polyvinyl alcohol or vinylalcohol copolymers, wherein if the polyvinyl alcohol or vinyl alcoholcopolymers are present in the drilling fluid, the weight ratio of thesum of the polyvinyl alcohol or vinyl alcohol copolymers to the totalweight of the drilling fluid is less than or equal to 1.5:100; one ormore water-soluble acid catalyst precursors or the reaction products ofsuch water-soluble acid catalyst precursors, wherein the weight ratio ofthe sum of the one or more water-soluble acid catalyst precursors andthe reaction products of such water-soluble acid catalyst precursors tothe total weight of the drilling fluid is from 0.5:100 to 20:100; and abasic additive comprising sodium hydroxide, potassium hydroxide, orboth.
 2. The drilling fluid of claim 1, wherein the drilling fluidcomprises latex and the weight ratio of the latex to the total weight ofthe drilling fluid is less than or equal to 10:100.
 3. The drillingfluid of claim 1, wherein the one or more formaldehyde-based resinscomprise melamine-formaldehyde resin, urea-formaldehyde resin,phenol-formaldehyde resin, or combinations of these.
 4. The drillingfluid of claim 1, wherein the one or more water-soluble acid catalystprecursors comprise a water-soluble hydrolysable ester.
 5. The drillingfluid of claim 1, wherein the one or more water-soluble acid catalystprecursors comprise one or more of ethyl lactate, diethylene glycoldi-formate, ethyl acetate, ethyl formate, ethylene glycol diacetate,diethylene glycol di-lactate, or combinations of these.
 6. The drillingfluid of claim 1, wherein the reaction products of the water-solubleacid catalyst precursor comprise carboxylic acids.
 7. The drilling fluidof claim 1, wherein the base fluid comprises an aqueous solution.
 8. Thedrilling fluid of claim 1, wherein the base fluid comprises anon-aqueous solution.
 9. The drilling fluid of claim 1, furthercomprising one or more weighting agents, wherein the weight ratio of theone or more weighting agents to the base fluid is from 10:100 to300:100.
 10. The drilling fluid of claim 1, wherein the drilling fluidhas a density of from 50 pounds per cubic foot to 160 pounds per cubicfoot.
 11. The drilling fluid of claim 1, wherein the drilling fluid isin a gelled state such that the apparent viscosity at 300 rpm and 25° C.of the drilling fluid is greater than or equal to 50,000 centiPoise. 12.A sealed subterranean petroleum formation comprising: a subterraneanwellbore positioned adjacent a subterranean petroleum formation; and adrilling fluid positioned in the subterranean wellbore, the drillingfluid comprising: a base fluid comprising an aqueous or non-aqueoussolution; one or more formaldehyde-based resins, wherein the weightratio of the one or more formaldehyde-based resins to the base fluid isfrom 1:100 to 50:100; optionally polyvinyl alcohol or vinyl alcoholcopolymers, wherein if the polyvinyl alcohol or vinyl alcohol copolymersare present in the drilling fluid, the weight ratio of the sum of thepolyvinyl alcohol or vinyl alcohol copolymers to the total weight of thedrilling fluid is less than or equal to 1.5:100; one or morewater-soluble acid catalyst precursors or the reaction products of suchwater-soluble acid catalyst precursors, the weight ratio of the sum ofthe one or more water-soluble acid catalyst precursors and the reactionproducts of such water-soluble acid catalyst precursors to the totalweight of the drilling fluid is from 0.5:100 to 20:100; and a basicadditive comprising sodium hydroxide, potassium hydroxide, or both. 13.The sealed subterranean petroleum formation of claim 12, wherein thedrilling fluid is in a gelled state such that the viscosity of thedrilling fluid is greater than or equal to 50,000 centiPoise.
 14. Thesealed subterranean petroleum formation of claim 12, wherein thedrilling fluid comprises latex and the weight ratio of the latex to thetotal weight of the drilling fluid is less than or equal to 10:100.15.-21. (canceled)
 22. A drilling fluid comprising: a base fluidcomprising an aqueous or non-aqueous solution; one or moreformaldehyde-based resins, wherein the weight ratio of the one or moreformaldehyde-based resins to the base fluid is from 1:100 to 50:100;optionally polyvinyl alcohol or vinyl alcohol copolymers, wherein if thepolyvinyl alcohol or vinyl alcohol copolymers are present in thedrilling fluid, the weight ratio of the sum of the polyvinyl alcohol orvinyl alcohol copolymers to the total weight of the drilling fluid isless than or equal to 1.5:100; and one or more water-soluble acidcatalyst precursors or the reaction products of such water-soluble acidcatalyst precursors, wherein the weight ratio of the sum of the one ormore water-soluble acid catalyst precursors and the reaction products ofsuch water-soluble acid catalyst precursors to the total weight of thedrilling fluid is from 0.5:100 to 20:100, wherein the one or morewater-soluble acid catalyst precursors comprise one or more ofdiethylene glycol di-formate, ethyl acetate, ethyl formate, ethyleneglycol diacetate, diethylene glycol di-lactate, or combinations ofthese.
 23. The drilling fluid of claim 22, wherein the one or morewater-soluble acid catalyst precursors comprise diethylene glycoldi-formate.
 24. The drilling fluid of claim 22, wherein the one or morewater-soluble acid catalyst precursors comprise diethylene glycoldi-lactate.
 25. The drilling fluid of claim 22, wherein the one or morewater-soluble acid catalyst precursors comprises one or more of ethylacetate or ethylene glycol diacetate.
 26. The drilling fluid of claim22, wherein the one or more water-soluble acid catalyst precursorscomprise ethyl formate.
 27. The drilling fluid of claim 1, wherein theweight ratio of the basic additive to the base fluid is from 0.001:100to 5:100.